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Published in: TDI News Release
Date: February 2009


Liner Systems recognized by ASHRAE

Performance values for metal building insulation assemblies have been the focus of recent code development cycles within the ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers). As the metal building construction industry yields to the market pressure for more energy efficient buildings, ASHRAE has already made changes to the prescriptive requirements in their next 90.1 Standard supplement for metal building roofs and walls.

The ASHRAE 90.1 Standard, Energy Standard for Buildings Except Low-Rise Residential Buildings, is typically published every three years. The next full publication, Standard 90.1-2010, is targeted to achieve a 30% energy savings compared to the 90.1-2004 Standard. One area that the Building Envelope Committee is relying on to reach this goal is the envelope insulation requirements for metal building roofs and walls. The realization of changes for metal buildings become evident when ASHRAE released their eighteen-month supplement to 90.1-2007. There are a total of sixteen different approved addenda within this supplement, and one in particular that metal building contractors and designers need to become familiar with—Addendum G. This addition increases the stringency for metal building roofs by lowering the U-factor by approximately 20% throughout climate zones two through eight for conditioned metal buildings in the United States.

The prescriptive requirements for Addendum G will require more than the “traditional” method of insulating metal buildings. This method commonly uses single-layer fiberglass rolls installed perpendicularly over the purlins and girts, compressing the insulation when metal panels are installed. The new addendum expands the metal building roof assemblies listed in Table A2.3 “Assembly U-Factors for Metal Building Roofs” to include an assembly called “Liner System.” It showcases a total of six different liner system assemblies for screw down roofs and standing seam roofs.

Although liner systems have been used in metal buildings for over 25 years, this is the first time ASHRAE has incorporated them into the standard.

Although liner systems have been used in metal buildings for over 25 years, this is the first time ASHRAE has incorporated them into the standard. Previously, the only metal building insulation assemblies and performance values in the Standard were supplied and promoted by NAIMA (North American Insulation Manufacturers Association). These assemblies and values have been incorporated into each Standard since the 90.1-1999 version. Each of the liner system assemblies recently added outperform all of the previous assemblies that have been promoted by NAIMA and ASHRAE. As an example, a standing seam roof insulation assembly that incorporates a double layer construction of R-19+R-19 supposedly provides a U-factor of U-0.046 with no hot box verification, whereas hot box tests for a liner system of R-11+R-19 provide a verified U-factor of U-0.035.

Liner systems are superior to the traditional methods of insulating because they help address three crucial problems associated with over-the-top installation:

  1. Insulation Compression – traditional methods compress the insulation, minimizing actual thermal performance.
  2. Vapor Retarder Placement – traditional metal building insulation methods do not isolate the highly conductive steel purlins and girts from the conditioned space. Improper placement outside of the dew point line commonly results in condensation and corrosion problems.
  3. Proper Sealing of Vapor Retarder – traditional metal building insulation methods require the installer to “seal” consecutive runs of laminated fiberglass rolls. This is commonly done by aligning the tabs, rolling the tabs and stapling together. It is not uncommon for the staples and joints to deteriorate over time, increasing the opportunity for heat transfer.

A liner system assembly not only help address these three problems but it also provides a clean finished appearance, a higher acoustical performance and enhances the efficiency of the lighting systems. Liner systems can be installed from the topside or bottom side during new construction and works extremely well when retrofitting existing buildings.

In addition to Addendum G, ASHRAE is currently investigating the validity of the existing metal building insulation assembly U-factors for supplied by NAIMA that have been incorporated into the 90.1 Standard since 1999. This scrutiny is due to a series of hot box tests conducted at Oak Ridge National Laboratory, studies from the University of Illinois at Urbana-Champaign and field surveys of measured insulation thicknesses that show over-the-purlin NAIMA-published performance values are inflated by approximately 20% as typically installed.


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